It is well known that, an aromatic primary amine color developing agent oxidized with an exposed silver halide reacts with a coupler to form a dye such as an indophenol, an indoaniline, an indamine, an azomethine, a phenoxazine, a phenazine or a like dye, to thereby form a color image. In this type of photographic system, the subtractive color process is ordinarily employed for color reproduction and color images are formed using yellow, magenta and cyan dyes.
In order to form cyan color images, phenolic or naphtholic couplers are generally employed. However, color reproducibility is remarkably deteriorated since dyes formed from these couplers have undesirable absorption in the green light region.
In order to solve this problem, 2,4-diphenylimidazoles have been proposed as described in European Patent 249,453. These couplers are preferred for color reproduction since they provide dyes having less undesirable absorption on the shorter wavelength side in comparison with conventional dyes.
However, the couplers as described in European Patent 249,453 are disadvantages in practical use because they have a low coupling activity, the hue of the dyes formed therefrom is unsatisfactory and the dyes formed therefrom have very poor fastness to heat and light (image preservability).